The communion of saints is the Church (Catechism of the Catholic Church, No. 946). It has three states or divisions, the communion of saints of the living, those who are still on their pilgrim journey on earth; and the communion of saints of the dead or the faithful departed, some of whom are being purified, those in purgatory, and the ones who are enjoying eternal glory in the presence of God, those in heaven (Catechism, No. 954).
The living are “saints” because they are baptized, members of the Body of Christ, members of the church, unified in faith and belief, praying and receiving the sacraments, and advancing in holiness. Their sainthood is real but unfinished; “they are saints in training” or “saints in progress.”
The dead, or the faithful departed, are saints because their time on earth is over. They are the ones who have completed the race, kept the faith, and have been given the crown of righteousness (2 Timothy 4:7,8). When they stood before the Son of Man, they were judged to be righteous and told, “Come, you who are blessed by my Father. Inherit the kingdom prepared for you from the foundation of the world” (Matthew 25:34). They are the sheep for whom the Good Shepherd freely laid down his life (John 10:1-18); the ones who have been escorted by Jesus to the Father’s house (John 14:1-3); and the great multitude which no one can count that are gathered around God’s throne (Revelation 7:9).
from The CatholicSpirit.com
When Catholics say the word saint, they are usually talking about a specific kind of saint, a canonized saint. Catholics should probably be more explicit so as not to cause confusion.
The Church recognizes some Christians (saints) that have endured, entered Heaven and won the crown, and while there, have proven to be serious prayer warriors for us on earth. The Church must be convinced beyond a shadow of a doubt that the saint is in heaven. This is why they go through so much scrutiny over each and every saint. When they canonize someone they are really saying: "Hey, this person had a very cool relationship to the Lord while on earth and now they are in heaven and are really praying hard for us."
How are saints chosen by the Catholic Church?
There are over 10,000 named saints and beati from history, the Roman Martyology and Orthodox sources, but no definitive "head count".
How does the Church choose saints?
Canonization, the process the Church uses to name a saint, has only been used since the tenth century. For hundreds of years, starting with the first martyrs of the early Church, saints were chosen by public acclaim. Though this was a more democratic way to recognize saints, some saints' stories were distorted by legend and some never existed. Gradually, the bishops and finally the Vatican took over authority for approving saints.
from Catholic Online